464 R. E, BUCHANAN 



Genus 2. Beggiatoa Trevisan, 1842, p. 76 



Threads sheathless, formed of flat discoidal cells, not attached. 

 Midtiplication by transverse splitting of the threads. Showing 

 an undulating motion, creeping. Cells contain globules of sulphur. 

 Usually in hot sulphur springs. 



The type species is Beggiatoa alba (Vaucher) Trevisan. 



Genus 3. Thioploca Lauterborn, 1907, p. 238 



Filaments Beggiatoa-like, with numerous sulphur granules, 

 motile, lying parallel in considerable numbers, or united in bundles 

 enclosed in a colorless layer of gelatin. 



The type species, Thioploca schmidlei Lauterborn has fila- 

 ments 5 to O/x thick, and gelatinous sheath 50 to 160^ thick. 

 From the ocean bed. 



Family III. Rhodobacteriaceae Migula, 1900, p. 1042 



Synonym : 



Rhodobacteria Molisch, 1907, p. 27 



Cells of various types, not filamentous, containing bacterio-pur- 

 purin with or without sulphur granules also. 



Two subfamilies may be separated by the following key : 



Ke]j to the subfamilies of Rhodobacteriaceae 



A. Cells containing sulphur granules Subfamily I. Chmmatioideae 



B. Cells without sulphur granules Subfamily II. Rhodobacterioideae 



Subfamily I. Chromatioideae Nom. nov. 



Synonyms : 



Thiorhodaceae Molisch, 1907, p. 28 



Cells .not filamentous, containing both sulphur granules and 

 bacteriopurpurin. 



The following names have been used for genera in. this group: 



Erythroconis Oersted, 1842, p. 552 

 Chromatium Perty, 1852, p. 179 

 Clathrocystis Henfrey, 1856, p. 53 

 Rhabdomonas, Cohn, 1875, p. 167 



